Household video technology began decades ago with an analog station-transmitted video signal, a roof top antenna, and a three channel black and white television set in a living room. Since then, video technology has experienced rapid growth due to advances in microprocessor, communications, and digital signal processing technology. In addition to the standard television, the video market has expanded to include video cassette recorders (VCR), multiple providers of satellite television, digital cable, video on-demand cable, digital television, hi-definition television, overhead projection television, home movie theaters, camcorder video units and many other video options. As technology continues to develop, the list of video options available to the consumer will continue to grow as well.
The vast video market has led to an expansion of video formats currently in use by these different products. In fact, some products have more than one video format. For example, digital television transmission has been approved and is in operation in the United States. The standard for digital television includes 18 new video formats.
The increasing number of video products and corresponding video formats has created a problem of compatibility between products. In order to experience video from one format in another format, the video stream must be processed and transformed into the desired format. For example, to view video formatted according to the interlaced scanning scheme used in analog television standards on a computer display that uses progressive scanning, a format transformation must be performed.
Before this transformation occurs, a video signal and it's corresponding audio signal are synchronized to temporally correspond to each other. As a result of the format transformation, the required signal processing introduces an undesirable delay in the video stream, causing the video and audio streams to be unsynchronized. That is, as a result of the transformation, conversations and sound effects in the video may not match a speaker's mouth or events as they occur. Furthermore, as signals are processed through more than one device, this delay becomes greater and more noticeable to the viewer. The transformation processing therefore requires that the video and audio signal be re-synchronized to eliminate the undesirable mismatching of the video and audio signals.
A delay introduced in the audio signal provided to synchronize the audio and video signal is dependent upon the format of the video and corresponding audio signal. As discussed above, a number of formats are used for digital video signals. These formats accommodate variable audio sampling rates and sample sizes. Furthermore, digital audio signals are commonly transported from one processing device to another within an audio/video processing product using a number of serial transmission schemes. These schemes use various methods to mark the start of a sample or determine left from right in a stereo pair. One example of such a serial audio stream is a standard known as I2S. As such, different types of digital audio signals require a different delay in order to be properly re-synchronized to their corresponding processed video signal.
Circuits that adjust an audio signal to account for the delay required by video signal processing are well known in the art. However, past solutions of the prior art consist of circuits that provide a delay in the audio signal only for video transformed from one specific format to another. In order to provide the appropriate audio delay for different video format transformations using the solutions in the prior art, several circuits are required as shown in FIG. 1. This solution requires additional hardware and adds expense to the consumer. Furthermore, in many practical cases, the processing device which converts the video formats may have no information regarding which audio format is in use, thus providing an improper delay or otherwise impairing the synchronization process.
What is needed is an apparatus that can determine the digital serial audio format in use, and then automatically delay the serial digital audio stream to synchronize the audio and video streams.